IndexError: list index out of range for CSV

Question

I am currently working on an Inventory System, and have just developed code that allows me to add items to my.csv

My current csv file looks like this:

Here is my relevant code:

class CsvReader:
    def __init__(self): 
        self.result = []

    def make_dict_items(self):
        #fn = os.path.join('subdir', "Items2.csv")
        with open("Items2.csv") as fp:
            reader = csv.reader(fp)
            labels = next(reader, None)
            result = []
            for row in reader:
                row[0] = int(row[0])
                row[1] = float(row[1])
                row[2] = int(row[2])
                pairs = zip(labels, row)
                self.result.append(dict(pairs))

    def show_available(self):
        for item in self.result:
           print(item)
        
    def add_item(self):
       item_num = int(input("What is the items #?\n"))
       price = float(input("What is the items price?\n"))
       quant = int(input("What is the items quantity?\n"))
       name = input("What is the items name?\n")
       new_row = [item_num, price, quant, name]
       with open("Items2.csv", "a+") as  fp:
           reader = csv.reader(fp)
           fp.seek(0)
           labels = next(reader, None)
           writer = csv.writer(fp)
           new_record = dict(zip(labels, new_row))
           self.result.append(new_record)
           writer.writerow(new_record.values())

From what I understand, my add item is able to successfully input into my csv. For example, if I input 1, 2.99, 3, and Pumpkin into the inputs, and print(system.result), I can see the new dictionary in the list, and visually see it if I were to open the csv document.

What I dont understand is my current error I am getting. When I try to view my new item with my existing method that shows all items, I get an error:

row[0] = int(row[0])
IndexError: list index out of range

I understand this error has to do with trying to call elements in a list that don't exist, but what seems to be the issue here. Why when I have the four items in my csv, the code works fine, but when I add a new row into the csv file, the code fails? Why does that specific line in make_dict_items not work when a 5th item is added, but works with the beginning four?

Answer 1

Your CSV has blank lines, which create empty row . Check for this and skip it.

            for row in reader:
                if row:
                    row[0] = int(row[0])
                    row[1] = float(row[1])
                    row[2] = int(row[2])
                    pairs = zip(labels, row)
                    self.result.append(dict(pairs))

Answer 2

I would also suggest looking into something like dataclasses and dataclass-csv for this, just to align with best practices in Python and to also to streamline the task, and make it easier to work with the data.

For example, here's a working sample I was able to test with. This works with pip install dataclass-csv to install the library beforehand.

from dataclasses import dataclass

import dataclass_csv


@dataclass
class MyClass:
    item_no: int
    price: float
    quantity: int
    name: str


with open('Book.csv') as f:
    reader = dataclass_csv.DataclassReader(f, MyClass)

    reader.map('Item #').to('item_no')
    reader.map('Price').to('price')
    reader.map('Name').to('name')
    reader.map('Quantity').to('quantity')

    for line in reader:
        print(line)

Notice here how the type annotations such as price: float indicate that the type of the field should be float for example.

The output of the above code is as follows:

MyClass(item_no=1, price=5.99, quantity=1, name='Blueberry Muffin')
MyClass(item_no=2, price=6.99, quantity=2, name='Bannana-nut Muffin')
MyClass(item_no=3, price=7.99, quantity=3, name='Chocolate Chip Cookie')
MyClass(item_no=4, price=8.99, quantity=4, name='Oatmeal Cookie')